Documentation
LifePatch
Overview
LifePatch is a proposed wearable health-monitoring system designed to make routine biomarker monitoring more convenient and less disruptive. It is intended primarily for elderly people and busy adults who may find conventional health checks inconvenient because of blood draws, lengthy appointments, complicated equipment, or missed follow-ups.
The device is designed as a compact upper-arm wearable. Instead of requiring a conventional blood sample, LifePatch uses a microneedle-based interface to access interstitial fluid (ISF) beneath the skin. The sensing system then performs electrochemical measurements of three selected biomarkers: glucose, total cholesterol, and creatinine.
LifePatch is designed for on-demand measurements. The user selects the desired measurement, the corresponding sensing channel is activated, and the resulting data is processed by the device before being transmitted to a smartphone through Bluetooth Low Energy (BLE).
The smartphone application provides the user with the resulting numerical measurement, previous measurements, trends, alerts, and simplified explanations.
LifePatch is a proposed monitoring technology, not a clinically validated diagnostic device. Its purpose is to provide accessible health information while recognising that laboratory testing and professional medical assessment remain necessary.
System Architecture
LifePatch consists of three interconnected systems:
The wearable system is responsible for interacting with the user's skin and detecting the selected biomarkers.
The electronic system controls the sensing process, measures the electrochemical signals, processes the data, manages power, and communicates wirelessly.
The digital system receives the measurements on a smartphone and presents them in a form that the user can understand.
The overall architecture is:
Skin → Microneedles → Interstitial Fluid → Biomarker Sensor → Electrochemical Signal → AD5940 → nRF52840 → Bluetooth Low Energy → Smartphone Application
The physical wearable itself is divided into five main layers:
- Outer shell
- Electronics layer
- Sensor layer
- Adhesive layer
- Microneedle layer
The electronics are designed to be reusable, while the biological sensing components are incorporated into a replaceable cartridge. This prevents the entire device from having to be discarded when the components that contact skin and biological fluid need replacement.
Why Interstitial Fluid Is Used
A major part of the LifePatch design is the decision to measure interstitial fluid rather than directly extracting blood.
Interstitial fluid surrounds the cells within the body's tissues and contains many small molecules that can be measured as indicators of physiological conditions. Accessing this fluid allows the device to perform minimally invasive measurements without functioning like a conventional blood-drawing needle.
The microneedles therefore do not exist to collect a conventional blood sample. Their purpose is to cross the outer skin barrier and establish access to the interstitial fluid, allowing the sensing regions to interact with the biomarkers contained within it.
This is particularly important for the design because LifePatch is intended to be small and convenient. A system that required conventional blood extraction would introduce additional requirements for fluid extraction, collection, handling, and disposal.
However, ISF measurements should not automatically be interpreted as identical to blood measurements. The relationship between ISF and blood concentrations can depend on the biomarker and physiological conditions. This is one reason LifePatch is positioned as a monitoring system rather than a replacement for laboratory testing.
Reusable Body and Replaceable Cartridge
One of the most important design decisions is the separation between the reusable electronic body and the replaceable biological cartridge.
The reusable body contains components such as the microcontroller, electrochemical analogue front end, multiplexer, battery, charging circuitry, PCB, wireless communication hardware, and protective housing.
The replaceable cartridge contains the microneedles, sensing electrodes, recognition chemistry, membranes, ISF interface, and skin-contact components.
The biological components should not simply be cleaned and reused indefinitely. Repeated use could result in contamination, biofouling, degradation of enzyme-based sensing chemistry, sensor drift, and inconsistent measurements.
The cartridge system therefore allows the biologically exposed components to be replaced while preserving the more expensive electronic components.
Outer Shell
The outer shell provides the physical protection and structural support for the LifePatch.
The proposed housing uses medical-grade polycarbonate (PC) because the material needs to be lightweight while providing mechanical protection to the electronics.
A medical-grade silicone gasket/O-ring is incorporated around appropriate housing interfaces to help protect the internal electronics from sweat and moisture.
The device also contains a WS2812B-Mini RGB LED. This functions as a simple status indicator, allowing the device to communicate conditions such as normal operation, an error, or low battery without requiring the user to immediately open the application.
Because the LED sits inside the housing, a clear polycarbonate light pipe carries its illumination through the outer casing.
The replaceable cartridge is mechanically secured using a cartridge latch. Electrical communication between the cartridge and reusable electronic body is established through gold-plated pogo-pin contacts.
Electronics
The electronics are responsible for converting the small electrical responses generated by the biosensors into usable digital information.
nRF52840 Microcontroller
The Nordic nRF52840 functions as the main microcontroller.
It coordinates the LifePatch system, including measurement control, signal processing, power management, memory, and wireless communication.
Its integrated Bluetooth Low Energy capability allows the device to communicate with the smartphone without requiring a physical cable.
The nRF52840 therefore acts as the central controller connecting the sensing hardware to the digital application.
AD5940 Electrochemical Front End
The Analog Devices AD5940 is the main electrochemical analogue front end and potentiostat.
The biosensors do not directly output a digital value such as “glucose = 5.2.” Instead, their chemical reactions produce very small electrical responses.
The AD5940 provides the circuitry required to control the electrochemical measurement and measure those responses accurately enough for subsequent processing.
The signal therefore follows a progression from:
Biochemical reaction → electrical response → AD5940 measurement → digital processing
ADG704 Multiplexer
The Analog Devices ADG704 analogue multiplexer allows the electronic system to select between the three biomarker channels.
Instead of requiring a completely independent measurement circuit for every biomarker, the multiplexer allows the common electrochemical measurement electronics to connect to the selected sensing channel.
For example, if the user requests a glucose measurement, the system connects the glucose sensing region. If the user subsequently requests cholesterol, the measurement pathway switches to the cholesterol channel.
TMP117 Temperature Sensor
The Texas Instruments TMP117 measures temperature near the device.
Temperature can influence electrochemical measurements, so recording the temperature provides information that may be used during measurement processing or compensation.
Memory
The nRF52840 provides internal memory for device operation and data.
An optional Winbond W25Q32JV SPI flash memory can provide additional storage for measurement history if the application requires the wearable itself to retain larger quantities of data.
PCB
The electronic components are integrated onto a proposed four-layer rigid-flex PCB.
The PCB provides the electrical traces required to connect the microcontroller, electrochemical front end, multiplexer, temperature sensor, power circuitry, memory, battery, LED, antenna, and cartridge contacts.
The rigid-flex structure is proposed because LifePatch must fit into a relatively small wearable enclosure while maintaining reliable electrical connections.
Power System
LifePatch uses a proposed 3.7 V, approximately 300 mAh lithium-polymer battery.
The battery supplies energy to the microcontroller, electrochemical measurement circuitry, sensors, wireless communication, and other electronic components.
The TI BQ24074 functions as the battery-charging IC. It controls the charging process when the device is connected to its charging source.
The TI TPS63031 buck-boost regulator provides regulated power to the electronics even as the battery voltage changes during discharge.
The device uses dedicated charging contacts so that charging can occur through the reusable electronic body without requiring the biological sensing cartridge to remain attached.
Electrochemical Sensor Architecture
The sensor layer contains three independent sensing channels.
Each channel uses a three-electrode electrochemical configuration:
Working electrode: the primary surface where the target reaction is measured.
Reference electrode: provides a stable reference potential for controlling the electrochemical measurement.
Counter electrode: completes the electrical circuit and allows current to flow during the electrochemical measurement.
Keeping the three biomarker sensors separate is important because glucose, cholesterol, and creatinine require different recognition mechanisms. A single generic sensing chemistry cannot simply be assumed to detect all three reliably.
Glucose Sensor
The glucose sensing system uses glucose oxidase (GOx) as its recognition element.
When glucose reaches the sensing layer, GOx catalyses its oxidation. One important product of this reaction is hydrogen peroxide.
The sensing process can be simplified as:
Glucose → GOx reaction → H₂O₂ → electrochemical detection → electrical signal
The LifePatch concept uses a Prussian Blue detection layer to facilitate electrochemical detection of the hydrogen peroxide.
The proposed electrode structure consists of a platinum or gold working electrode, Ag/AgCl reference electrode, and platinum counter electrode.
The GOx is maintained at the sensing interface using a chitosan + glutaraldehyde immobilisation layer.
The concentration of glucose reaching the sensing region affects the resulting electrochemical response, which is measured by the AD5940 and processed by the nRF52840.
Cholesterol Sensor
The cholesterol sensor uses cholesterol oxidase (ChOx).
ChOx interacts with cholesterol and generates an electrochemically detectable response.
The proposed electrode system contains a platinum working electrode, Ag/AgCl reference electrode, and platinum or silver counter electrode.
The sensing interface uses BSA and Nafion. BSA can contribute to the immobilisation of the sensing chemistry, while Nafion can act as a selective interface that helps reduce interference from other substances in biological fluid.
The LifePatch cholesterol design is based on existing microneedle-based electrochemical cholesterol research rather than simply copying the glucose sensor and changing the enzyme.
Creatinine Sensor
Creatinine was selected as the third biomarker because it is an important kidney-health biomarker.
The proposed creatinine sensing region contains a gold working electrode, Ag/AgCl reference electrode, platinum counter electrode, creatinine-selective recognition layer, and Nafion anti-interference membrane.
The important technical distinction is that the physical architecture has been specified, but the exact creatinine recognition chemistry has not been finalized as a validated LifePatch component.
This should remain explicitly stated in the README. Claiming a specific recognition chemistry as fully developed would imply experimental validation that the current LifePatch project does not have.
The creatinine channel should therefore be described as a proposed research-based sensing architecture requiring further experimental development and validation.
Microneedle System
The microneedle system is the physical interface between LifePatch and the interstitial fluid.
The proposed microneedles use methacrylated hyaluronic acid (MeHA) and hyaluronic acid (HA) in a crosslinked polymeric structure.
The current proposed geometry is a 3 × 5 array containing 15 microneedles, with an approximate height of 600–800 µm.
These dimensions are design proposals rather than experimentally validated final specifications.
The microneedles are intended to penetrate the outer skin barrier and access ISF without functioning as conventional blood-drawing needles.
A polycarbonate microneedle base supports the array. An ISF collection interface or hydrogel can facilitate contact between the interstitial fluid and the electrochemical sensing regions.
The sensing area is divided into three regions so that glucose, cholesterol, and creatinine each have a dedicated sensing environment.
Adhesive Layer
The adhesive layer keeps LifePatch positioned correctly against the upper arm.
It consists of a medical-grade polyurethane backing film combined with a medical-grade acrylic adhesive.
A laser-cut central microneedle opening allows the microneedles to access the skin while the surrounding adhesive holds the device in place.
Because this layer contacts the user and forms part of the biological interface, it belongs to the replaceable portion of the system.
Complete Measurement Process
The measurement process begins when the user attaches LifePatch to the upper arm.
The microneedles penetrate the outer skin barrier and establish access to interstitial fluid.
The user then selects the desired biomarker through the LifePatch application.
The nRF52840 receives the measurement request and activates the corresponding sensing pathway. The ADG704 connects the selected sensor channel to the electrochemical measurement circuitry.
The target biomarker reaches its corresponding recognition chemistry.
For glucose, GOx reacts with glucose and produces hydrogen peroxide, which is detected using the Prussian Blue-based electrochemical interface.
For cholesterol, ChOx provides the biomarker-specific reaction at the cholesterol sensing region.
For creatinine, the dedicated creatinine-selective sensing layer interacts with the target molecule.
In every case, the biochemical interaction produces a small electrical response.
The AD5940 measures that response.
The nRF52840 receives and processes the measurement data.
The temperature information from the TMP117 can be incorporated into the processing where appropriate.
The final processed result is transmitted through Bluetooth Low Energy to the smartphone.
The entire pathway is:
Skin → Microneedles → Interstitial fluid → Recognition chemistry → Electrochemical reaction → Electrodes → AD5940 → nRF52840 → BLE → Smartphone
Smartphone Application
The smartphone application provides the user-facing side of LifePatch.
A QR code can be used during initial setup to direct the user to the LifePatch application or configuration process. Once the wearable is paired, the device communicates with the application through Bluetooth Low Energy.
The application can display the current numerical measurement, previous measurements, trends, alerts, and simplified explanations.
The purpose of the software is to translate a complicated electrochemical measurement into understandable information.
For example, instead of presenting the user with raw electrical current data from the electrochemical sensor, the application would process that signal into a biomarker measurement and present it in an accessible format.
The application may also provide basic contextual guidance and indicate when a result may warrant professional assessment. It should not present itself as independently diagnosing a disease.
Hardware Summary
The complete hardware system consists of the following:
Outer shell
Medical-grade polycarbonate housing, medical-grade silicone gasket/O-ring, WS2812B-Mini RGB LED, clear polycarbonate light pipe, mechanical cartridge latch, and gold-plated pogo-pin cartridge contacts.
Electronics
Nordic nRF52840, Analog Devices AD5940, Analog Devices ADG704, Texas Instruments TMP117, optional Winbond W25Q32JV flash memory, 3.7 V ~300 mAh Li-Po battery, TI BQ24074 charging IC, TI TPS63031 buck-boost regulator, four-layer rigid-flex PCB, PCB traces, battery connectors, pogo-pin contacts, and charging contacts.
Glucose sensing
GOx, Prussian Blue, platinum/gold working electrode, Ag/AgCl reference electrode, platinum counter electrode, and chitosan + glutaraldehyde immobilisation layer.
Cholesterol sensing
ChOx, BSA + Nafion interface, platinum working electrode, Ag/AgCl reference electrode, and platinum/silver counter electrode.
Creatinine sensing
Creatinine-selective recognition layer, Nafion anti-interference membrane, gold working electrode, Ag/AgCl reference electrode, and platinum counter electrode.
Adhesive interface
Medical-grade polyurethane backing film, medical-grade acrylic adhesive, and laser-cut microneedle opening.
Microneedle interface
Crosslinked MeHA/HA microneedles, proposed 15-microneedle 3 × 5 array, proposed 600–800 µm height, polycarbonate base, ISF collection interface/hydrogel, and separate sensing regions for the three biomarkers.
Final Architecture
LifePatch can ultimately be understood as a reusable electronic platform combined with a replaceable biological sensing cartridge and a smartphone application.
The reusable body handles power, electrochemical measurement, processing, storage, and wireless communication. The cartridge handles the direct interaction with the skin and interstitial fluid. The smartphone provides the interface through which the user receives and understands the resulting measurements.
The complete system is designed around three biomarkers — glucose, total cholesterol, and creatinine — and uses microneedle-based access to ISF combined with biomarker-specific electrochemical sensing.
The concept's central objective remains simple:
make health monitoring easier to access without pretending to replace clinical healthcare.
The technical complexity stays inside the patch; from the user's perspective, the intended experience is simply attach the patch, select a measurement, and receive understandable health information on the phone.
